The invention relates to a liquid filter, in particular an oil filter for an internal combustion engine, comprising a filter housing, comprising a ring filter insert, which is arranged therein so as to be replaceable, and comprising a removable cover, which closes the filter housing during operation, wherein the filter housing encompasses at least one inlet for raw liquid to be filtered, which empties into a raw side of the filter housing, and a return, which starts at a clean side of the filter housing, for filtered clean liquid, wherein an eccentric outlet is arranged in a bottom of the filter housing for emptying the filter housing when the ring filter insert is removed, wherein the ring filter insert consists of a hollow-cylindrical filter material body, which is surrounded on the front side by front panels and which separates the raw side and the clean side from each another, wherein an eccentric blocking element for the outlet is arranged on the front panel facing the bottom, and wherein interacting positioning means are provided on the ring filter insert and on the filter housing, which bring the blocking element into engagement with the outlet when the ring filter insert is inserted into the filter housing.
A first liquid filter of the afore-mentioned type is known from DE 39 03 675 C2. This document shows an oil filter comprising a filter housing and a ring filter insert, which is arranged therein so as to be capable of being replaced. On its lower front panel, the ring filter insert has an eccentric bolt as closure for an eccentric outlet, which is provided in the bottom of the filter housing and which provides for an emptying of the filter housing in response to a replacement of a filter insert. Provision is made on the ring filter insert and on the filter housing for interacting positioning means, which only allow for an axial insertion of the filter insert in a position, which orients the bolt towards the opening of the outlet. Preferably, the positioning means are axially engaging groove and spring means, which are matched to one another, whereby the spring is provided in the filter housing as a rib, which protrudes radially inward, and the groove is provided in the circumference of the lower front panel of the ring filter insert.
It is to be considered to be a disadvantage of this known filter that, in response to the installation of the ring filter insert into the filter housing, an operator must actively establish the correct rotational position between these two parts, wherein experience shows that errors can be made easily.
A further relevant liquid filter is known from EP 1 229 985 B1. This document also shows a liquid filter comprising a filter housing a ring filter insert. On its lower front panel, the ring filter insert has an eccentric bolt for closing an outlet, which is arranged eccentrically in the bottom of the filter housing and through which the filter housing is emptied when the filter insert is replaced. A ramp, which runs circularly, which points upwards, which is embodied so as to slope in the direction of the outlet, and via which the bolt slides into the outlet by rotating the ring filter insert about itself, is embodied on the bottom of the filter housing.
It is disadvantageous here that the bottom of the filter housing is occupied with the ramp and that thus hinders the arrangement of other elements, such as channels or valves, which are required for the functioning of the liquid filter, or which even makes it impossible.
A third liquid filter of the afore-mentioned type is described in DE 103 53 424 A1. In the case of this liquid filter, the corresponding ring filter insert also has an eccentric bolt on its lower front panel as first press-lock element for closing an outlet as second press-lock element. Provision is furthermore made on the ring filter insert and on the filter housing for interacting guide means for a closable orientation of the two press-lock elements, wherein the guide means and the press-lock elements are embodied separately from each other. Preferably, the one guide means is a circular guide track comprising a circumferential interruption in the form of an axial slot and the other guide means is a stop, which can be inserted into the axial slot. The guide track can thereby be inclined, preferably with an incline, which corresponds to the thread pitch of a screw cap of the filter housing. Preferably, the guide track is provided on the bottom side of the lower front panel of the ring filter element.
The overall size of this known filter insert is markedly extended by means of the guide means, which requires an enlarged filter housing when maintaining the filter surface, or which leads to a reduction of the filter surface of the filter insert when the size of the filter housing stays the same.